One thing about being a CFI, is you will learn more than you were taught, just from the observation etc..... It's not probably going to be "cheap" per say to get the rating, and on the same note, it'll take awhile to pay for the loan or however you pay for it. Having the desire to teach and share the experience aviation gives you is the key. As far as getting the ticket, I see nothing wrong with the add-on through a 141 like ATP. Every new instructor is going to have problems teaching and working with students, it'll take 200+hrs of dual given in my opinion before you really start becoming solid in your teaching skills, and techniques. I've modified mine as I go, and with over 1000hrs of dual given, I still keep my mind open on differing techniques and ways to pass on the knowledge. The last thing I'll say is make sure you(and the student) are having fun, because yes it can be work, but flying for 99% of the people out there is for the enjoyment factor, so as soon as they stop having fun, they are more likely to drop out of it. Good luck, hope it goes well.